Oak Ridge National Laboratory

Physics Division

Physics Division Seminars

Physics Division Seminars bring us speakers on a variety of physics related subjects. Usually these are held in the Building 6008 large Conference Room, at 3:00 pm on the chosen day, but times and locations may vary. For more information, contact our seminar chairman,

Alfredo Galindo-Uribarri
Tel (Office): (865) 574-6124  (FAX): (865) 574-1268

Mon., August 02, 2004, at 3:00 p.m.

Deep-inelastic collisions with stable and radioactive beams: accessing very neutron-rich nuclei and probing the density dependence of the nuclear symmetry energy

George A. Souliotis, Cyclotron Institute, Texas A&M University
6008 Conference Room

Neutron-rich nuclides have traditionally been produced in spallation reactions, fission and ``cold'' projectile fragmentation. Apart from these main production approaches, the search for new synthesis routes is currently of great importance. At the Cyclotron Institute of Texas A&M University, we initiated a study of the production cross sections of neutron-rich isotopes from deep-inelastic collisions of neutron-rich beams on heavy neutron-rich targets. Recently, the reaction of 25-MeV/nucleon 86Kr on 64Ni and 124,112Sn targets was studied using the MARS recoil separator [1]. We observed a large enhancement in the production of neutron-rich fragments in the reactions of the 86Kr beam at 25-MeV/nucleon with the neutron-rich 64Ni and 124Sn targets relative to high-energy fragmentation reactions (as predicted by the EPAX parametrization).

Simulations using a deep-inelastic transfer (DIT) code indicate that the neutron skins of the neutron-rich targets play an important role. From a practical viewpoint, such reactions at these (or lower) energies offer a novel way to access very neutron-rich rare isotopes.

In parallel to the production studies, efforts to access information relevant to the properties of the nuclear equation-of-state (EOS) via heavy-residue isotopic scaling (isoscaling) are being pursued [2]. First, an approach to study the process of N/Z equilibration based on heavy-residue isoscaling has been recently developed [3]. This approach can provide a detailed testing ground of transport codes in which properties of the nuclear equation of state are of key importance and can thus be probed by detailed comparisons of calculations with data.

Second, we are currently working on an approach to study the density dependence of the nuclear symmetry energy employing isoscaling of heavy fragments produced close to the ultifragmentation threshold. Fragment excitation energies (obtained from velocities) are used to infer the density of the fragmenting quasi-projectiles. Under the scenario of an expanding Fermi gas at a given excitation energy, the value of the symmetry energy is obtained from isoscaling. A correlation of the symmetry energy with respect to density is obtained and compared with parametrizations. The importance of the results to the field of astrophysics (e.g. modeling of supernovae and neutron stars) will be pointed out.

Finally, possibilities to extend the above studies using neutron-rich radioactive beams at existing (or planned, see also [4]) radioactive beam facilities and, in the far future, at the proposed Rare Isotope Accelerator Facility (RIA) in the US will be outlined. [1] G.A. Souliotis et al., Phys. Rev. Lett. 91 (2003) 022701; Phys. Lett. B 543 (2002) 163; and Nucl. Instrum. Methods B 204 166 (2003).
[2] G.A. Souliotis et al., Phys. Rev. C 68 024605 (2003).
[3] G.A. Souliotis et al., Phys. Lett. B 588 (2004) 35.
[4] `A Proposed Facility Upgrade for the Texas A&M Univ. Cycloton Institute', accessible at: http://cyclotron.tamu.edu

host: K. Rykaczewski